Seafloor bacteria "feed" on Earth's oceanic crust

Washington, May 29 : A new study has determined that seafloor bacteria on ocean-bottom rocks appear to "feed" on the planet's oceanic crust.

The study was carried out by scientists from the Woods Hole Oceanographic Institution (WHOI) in Massachusetts, University of Southern California (USC) in Los Angeles, and other institutions.

While seafloor microbes have been detected before, this is the first time they have been quantified.

According to the study, the seafloor's rocky regions, once considered a barren plain dotted with hydrothermal vents, appear to be teeming with microbial life.

Using genetic analyses, Cara Santelli of WHOI, Katrina Edwards of USC, and colleagues found three to four times more bacteria living on exposed rock than in the waters above.

"Initial research predicted that life could in fact exist in such a cold, dark, rocky environment," said Santelli. "But we really didn't expect to find it thriving at the levels we observed," she added.

Surprised by this diversity, the scientists tested more than one site and arrived at consistent results, making it likely, according to Santelli and Edwards, that rich microbial life extends across the ocean floor.

"This may represent the largest surface area on Earth for microbes to colonize," said Edwards.

"These scientists used modern molecular methods to quantify the microbial biomass and estimate the diversity of microbes in deep-sea environments," said David Garrison, director of the National Science Foundation's (NSF's) Biological Oceanography Program.

"We now know that this remote region is teeming with microbes, more so than anyone had guessed," he added.

Santelli and Edwards also found that the higher microbial diversity on ocean-bottom rocks compared favorably with other life-rich places in the oceans, such as hydrothermal vents.

With evidence that the oceanic crust supports more bacteria than overlying water, the scientists hypothesized that reactions with the rocks themselves might offer fuel for life.

In the lab, they calculated how much biomass could be supported by chemical reactions with the rocky basalt. They then compared this figure to the actual biomass measured.

"It was completely consistent," said Edwards.

This discovery lends support to the idea that bacteria survive on energy from Earth's crust, a process that could add to our knowledge about the deep-sea carbon cycle and the evolution of life.

The newfound abundance of seafloor microbes makes it possible that early life thrived - and perhaps began on the seafloor.

"If we can really nail down what's going on, there are significant implications," said Edwards.

"I hope that people turn their heads and notice: there's life down there," he added.